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Bulletin de la Société géographique de Liège, 29, 1993, 97-104.
Crisite - a new minerai species found in the Bolhac cave
(Pådurea Craiului mountains, Romana)
Lucre ţ ia GHERGARI & Bogdan P. ONAC
Abstract
A white, sometimes yellow-brownish, gelatinous sediment found in the Bolhac cave was studied in laboratory
(microscopy, chemical composition, X-ray analysis, IR spectroscopy, therm o-analysis). It is a new amorphous
minerai assigned to the group of hydrated aluminium sulphate-silicates and should be called "crisite".
Résumé
Dans la grotte de Bolhac, on a trouvé un sédiment gélatineux de couleur blanche, parfois jaune-brunâtre.
Divers échantillons en ont été observés en laboratoire. La microscopie, l'analyse chimique, la diffractométrie,
le spectre infra-rouge et la thermo-analyse suggèrent qu'il s'agit d'un minéral nouveau, amorphe, du groupe
des silicates-sulfates hydratés d'aluminium. Il devrait être appelé "crisite".
I. GENERAL DATA
The Bolhac cave is located in the northern part of the
P å durea Craiului mountains, 2.5 km upstream from
uncuiu . The entrance, situated only 1 m above the
level of şCri ul Repede River, is an impressive arcade
of 33 x 20 m,
ş opening in the left bank of the river, at
the altitude of 307 m.
The cave is cut in marblish white Ladinian limestone
(Fig. 1). The limestone is unconformably and
transgressively overlain by Liassic sandstone and
quartzitic microconglomerates within which lensshaped kaolinitic clays, sometimes associated with
pyrite and marcasite, are to be found.
H. MORPHOGENETIC OUTLINE OF THE CAVE
V Å LEN Ş &
The Bolhac cave has a length of 554 m (V
IURKIEWICZ, 1981) out of which 320.5 m belong to
the main passage (Fig. 2). There is an underground
stream, 195 m long, with no affluents, for which we
assume an infiltrational source along the
limestone/sandstone boundary. The collecting area is
in fact a swamp formed by the waters coming from
old mining galleries, in the slope of Grosu hill. The
Å Ş
pH of these waters is strongly acid (3.3-4.1),
uncharacteristic for the karstic sources in the area.
Figure 1 : Map of Bolhac cave (simplified after
& IURKIEWICZ, 1978-1980)
1 water samples; 2 crisite samples; 3 limestone blocks
Téléchargé depuis / Downloaded from www.bsglg.be
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L. Ghergari & B.P. Onac
Figure 2 :
a) location of the studied area on the map of
Romania
b) geological map of the investigated area :
1. limestone (Ladinian) ; 2. sandstone (HettangianSinemurian) ; 3. pyritization ; 4. lapies ; 5. spring;
6. water samples ; 7. Bolhac cave ; 8. Napi ş tileu
rave
Figure 3 : Cross-section through the main gallery
1. limestone; 2. Sand; 3. blocks; 4. crisite;
5. water; 6. limestone blocks covered by crisite.
Crisite - a new minerai species found in the Bolhac cave (Pâdurea Craiului mountains, Romania)
99
For example, the waters of the Napi ş tileu cave (195 m
long, with a 71 m long underground stream), located
in the close vicinity, have a pH of 6.5. This high
acidity is caused by the oxidation of pyrite and
marcasite, fairly abundant in the sandstone cut by the
stream.
river bed white the submerged blocks are covered only
with 3-5 mm of the same material. The emerged
blocks have also an 1-3 mm thick crust formed by
under-water deposition during floods (Fig. 3). The
above mentioned moonmilk-type sediment also covers
the bed of a 2 m high waterfall.
III. DESCRIPTION OF THE GELATINOUS DEPOSIT
Detailed observations showed that the sediment is
thicker in the lower third of the underground stream
and in the arecs with pools; even the pools are close
to the sump which makes the source of the
subterranean stream. This indicates a transport of the
material in suspension during floods, from the upper
to the lower, flatter, sections of the cave, and also
explains the thicker deposits from the lower third, as
well as their presence on the emerged borders of the
stream.
All along the underground stream bed, covering both
sandy alluvia and its limestone borders, a layer of
white, sometimes yellow-brownish sediment can be
observed (Fig. 3).
The material of which the sediment is formed is jellylike in the water, easily dispersing when sampled.
The thickness of the sediment is of 1-3 cm on the
Figure 4 : Globular
cluster of Crisite
Figure 5 : Globular
cluster of Crisite;
goethite
100
L. Ghergari & B.P. Onac
IV. LABORATORY DATA
The analysis performed on samples collected from
varions locations in the cave (Fig. 2) showed the
following :
A. Microscopy
Under polarized light, the material behaves like an
isotropic, earthy mass, due to the very small size of
granules. TEM (transmission electronic microscope)
analysis shows a homogenous mass (more than 90%)
made up of agglomerates of tiny spheres, rarely
ovoids, with diameters ranging from 0.02 to 0.2 µ m,
specific for colomorphous minerals (Fig. 4, 5). Rare
(3-5%) xenomorphous equally thick and
semitransparent to electron beams lamellae, have also
been noticed ; only 2-3% of these lamellae revealed to
have a reticular structure when checked bv electron
diffraction. The diffraction pattern produced by
individual crystals, is characteristic for phylosilicates
with pseudohexagonal symmetry (probably illite).
Goethite prisms (1 - 2 %) are also present (0.2-1 pm).
B. Chemical composition
The chemical analysis revealed high contents of Al 203
and notable amounts of S0 3 , Si0 2 and H20+ (as main
components of the mineral) and 1( 20, mainly as
adsorbing ion. The rest of the oxides are present in
negligible amounts, and are considered to corne from
impurities (Table 1). The problem arising here is : are
the three main components gathered in one compound
or in distinct phases? An answer could be provided
by microprobe analysis (Fig. 6-8).
Table 1 : Chemical composition and thermic behaviour of the crisite.
Crisite - a new minerai species found in the Bolhac cave (P ådurea Craiului mountains, Romania)
101
It must be mentioned that the investigated layer is
made-up of superposed spherulites, therefore the data
obtained can not be rigorously assigned to a unique
phase. Silicon distribution in respect to aluminium is
relatively uniform, excepting some agglomerates, very
poor in aluminium, that we considered to be opal and
illite. We estimate opal does not exceed 1-2% in the
sample. An argument for the presence of SiO 4-4 in the
formula of the minerai is given by the presence of
mullite in the sample heated at 1000°C. Although the
uniform distribution of sulphur in the "X-ray image"
indicates the Jack of correlation between S0 2-4 and
A1 3+ ions, we consider that SO 2-4 is actually part of the
minerai formula, on the ground of the endotherms at
830°C and 880°C, characteristic of the decomposing
of aluminium sulphate.
Figure 6 : Electron microprobe analysis.
Al repartition
The formula of the minerai is :
The amount of water lost until 110°C varies according
to the dryness of the sample, ranging from 2 to 4 H 20.
C. X ray analysis
The X-ray analysis (diffractometry) shows the amorphous character of the sample. After heating at
1000°C, we obtained a spectrum characteristic of
mullite (Table 2) and probably for i-Al 2O3 (FOSTER,
1959).
-
D. IR spectroscopy
Figure 7 : Electron microprobe analysis.
Si repartition
The IR spectrum clearly shows the presence of H 20
and OH- . Absorption bands characteristic of S0 2-4
compounds, as well as of Si-O-Al and of Al-OH
bands, were also obtained. The line at 1445 cm -1 was
assigned to calcite (Fig. 9).
E. Thermie analysis
The DTA curve shows a double endotherm effect at
100°C, and 200°C respectively, and two close linked
endotherms at 830°C and 880°C, followed by the
exotherm at 940°C that marks the formation of
mullite. The fast two endotherms are the result of
water release, the following two ones marking the
release of OR, SO 3 and small amounts of CO 2
(Fig. 10).
Figure 8 : Electron microprobe analysis. S repartition
When testing the pH of the samples collected along
the underground Stream (Table 3), a slight
neutralization due to the buffer-effect of the limestone
was noticed, this parameter varying from 3.8 (at the
sump) to 4.6 (at the entrance), favouring thus the
precipitation of the Crisite from solution.
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L. Ghergari & B.P. Onac
Table 2 : X-ray diffraction spectrum of crisite, heated at 1000 ° C.
Table 3 : Chemical analysis of the water samples from Bolhac cave.
Crisite - a new mineral species found in the Bolhac cave (På durea Craiului mountains, Romania)
103
V. CONCLUSIONS
The analysis to which the white-yellowish minerai in
the Bolhac cave has been subjected, negate the
presence of allophane as we first thought. The
chemical formula, the thermie analysis, the electron
microscopy, microprobe and 1R spectroscopy are
pleading for the existence of a new amorphous minerai, assigned to the group of hydrated aluminium
sulphate-silicates, which we propose to be called
CRISITE ; it derives from the latin naine of the Cri ş ul
Repede River - Crisis. The first, and up to now the
only, occurrence of this minerai is the Bolhac cave,
which opens on the left bank of this river.
The crisite sample was deposited at the Mineralogy
Museum of the "Babeş-Bolyai" University in
Cluj—Napoca, Romania.
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L. Ghergari & B.P. Onac
Adresses des auteurs :
Lucreţia Ghergari
Université "Babeş-Bolyai"
Département de Minéralogie
1, Kogålniceanu str.
R-3400 CLUJ-NAPOCA
ROUMANIE
Bogdan P. Onac
Institutul de Speologie "Emil Racovi ţă "
Str. Clinicilor, nr. 5
R-3400 CLUJ-NAPOCA
ROUMANIE